Process for making heat-stabilized pentaerythritol tetranitrate



United States Patent 3,318,739 PROCESS FOR MAKING HEAT-STABILIZED PENTAERYTHRITOL TETRANITRATE H. William Voigt, Jr., Stanhope, N.J., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Nov. 4, 1966, Ser. No. 592,681 8 Claims. (Cl. 149-11) This invention relates to explosive compositions and more particularly concerns methods for making heatstabilized PETN explosives.

Pentaerythritol tetranitrate (PETN) has been used in such applications as boosters, squibs, initiators, blasting caps, sheet explosives, detonating cords, and the like. The undesirable heat stability characteristics of PETN however have prevented its general widespread use as a military explosive in this and many foreign countries.

For example, commercial PETN yields an excess of 11 ml. of gas within a 17 hour period from only a 2.3 gram sample when subjected to the 120 C. Vacuum Stability Test. Obviously, this instability of a high explosive such as PETN would render it generally unsafe for military applications in the field. It would be most advantageous for overall military purposes if methods could be devised wherein this material could be rendered heat stable.

It is therefore an object of this invention to provide a heat stable PETN explosive.

Another object of the invention is to provide methods for preparing heat-stable PETN explosives.

Other objects and features of this invention will become apparent as the invetnion is more fully hereinafter disclosed.

Briefly, I have discovered processes for rendering PETN sufiiciently heat stable by treating it with a solvent so as to reduce gassing of the PETN when subjected to elevated temperatures to such a degree that military stability requirements for this explosive are readily met.

More particularly, PETN may now be prepared such that a 2.3 gram sample, when subjected to the 120 C. Vacuum Stability Test for 20 hours will yield only about 1.20 ml. of gas and about 2.15 ml. of gas in a 40 hour period.

The 120 C. Vacuum Stability Test measures the sta bility of a material in ml. of gas liberated therefrom when subjected to a pressure of about mm. mercury at 120 C. for a period of time. The test is described in Military Specification, MIL-P-387A, Ian. 9, 1957, and in Standard Laboratory Procedures for Sensitivity, Brisance and Stability of Explosives, Arthur J. Clear, Feltrnan Research Laboratories, Picatinny Arsenal, Dover, N.J., January 1961, pages 25 to 30.

Military requirements specify that the maximum amount of gas to be evolved in a 20 hour period from a 2.3 gram sample of PETN at 120 C. shall not exceed 5 ml. In accordance with the objects and military requirements above-described, about to 50 weight percent of a commercial PETN, when dissolved in N-methyl- 2-pyrrolidone to form a solution, and which was poured into a suitable liquid to form a suspension, filtered, washed and dried, only 1.20 ml. of gas was evolved in a hour period at 120 C.

The following are illustrative examples of processes of my invention:

EXAMPLE I Coat 10 g. of a standard commercial dry PETN (conforming to Mil. Spec. MILP-387A, Jan. 9, 1957) with about 0.2 weight percent polyvinyl pyrrolidone (PVP) having a molecular weight of about 90,000 by dissolving the proper quantity of PVP in water or ethanol and then stirring the PETN thereinto and drying. The granulation "ice of the PETN is such that 100% will pass through a US. Standard Sieve No. 200, and which as received, then dried in vacuum at 50 C. for 4 hours, yielded 11+ ml. gas when subject to the 120 C. Vacuum Stability Test when using a 2.3 g. sample for a 20 hour period. Dissolve the coated PETN in 10 g. N-methyl-Z-pyrrolidone in a beaker placed on a steam bath, the N-methyl-Z-pyrrolidone solvent being maintained at 60-80 C. Pour the resultant solution slowly into a beaker containing about 50 ml. of rapidly agitated ethanol held at about 20 C. until a very fine, fuzzy-like suspension results. Filter the suspension on a Buchner filter using No. 54 filter paper. The solid collected is washed twice with about 50 m1. portions of ethanol. The washed collected solid is then air dried in a steam oven at about C. The dried PETN produced was of extremely fine particle size (15 microns). A 2.5 g. sample of this PETN produced 1.13 ml. gas in 20 hours and 1.59 ml. gas in 40 hours when subjected to the 120 C. Vacuum Stability Test.

EXAMPLE II The dry PETN is dissolved in N-methyl-2-pyrrolidone in a manner described under Example I, except:

1) 0.08 g. of PVP having a molecular weight of about 90,000, is co-dissolved with the PETN in the solvent, and

(2) 2-50 ml. portions of distilled water are used to wash the collected solid in lieu of ethanol. (Ethanol may be used satisfactorily however.)

A 2.5 g. sample of this PETN produced 1.29 ml. of gas in 20 hours and 1.63 ml. of gas in 40 hours when subjected to the 120 C. Vacuum Stability Test.

EXAMPLE III The dry PETN is coated, and dissolved in N-methyl-2- pyrrolidone solvent in a manner described under Example I with the following exception:

(1) 0.6 g. (6% by weight of the PETN) of a phenoxy resin having the structure r w r n L OH: H OH HlN -ioo and serving as a stabilizer and binder was co-dissolved with the solvent. A

(2) The solution was poured into about 50 ml. distilled water maintained at 16 C. to form a suspension having temperature of about 32 C.

(3) Wash the collected solid with 2-50 ml. portions of distilled water.

Results of 120 C. Vacuum Stability Test on a 2.5 g. sample showed 1.01 ml. and 1.84 ml. of gas evolved after 20 hours and 40 hours respectively.

EXAMPLE IV The dry PETN, uncoated with any PVP, is dissolved in N-methyl-Z-pyrrolidone solvent in a manner described under Example I except:

(1) PETN was dissolved in 20 g. solvent at a temperature of about 40 C.

2) Solution was poured into ml. distilled water at 20 C., resultant suspension temperature being 30 C.

(3) Collected solids were washed with 2-50 ml. portions distilled water.

For a 2.5 g. sample of PETN, the C. Vacuum Stability Test revealed 1.28 and 2.11 ml. of gas evolution for a 20 hour and 40 hour period respectively.

If in the preceding Example IV, acetone is substituted for N-methyl-2-pyrrolidone, about 35% PETN only may be dissolved therein whereas about 50% PETN may be readily dissolved in N-methyl-Z-pyrrolidone. Further, the gas evolution characteristics of the acetone-dissolved 3 PETN is slightly inferior to the N-methy-l-Z-pyrrolidonedissolved PETN.

My inventive process may be used advantageously in the stabilization of violent explosives such as mannitol hexanitrate EXAMPLE V 8 g. dry heat-unstable PETN and 2 g. mannitol hexanitrate (100% passing through a US. Standard Sieve, No. 200 were each precoated with 0.2% PVP (molecular weight about 90,000) and then dissolved simultaneously in 15 g. N-methyl-2-pyrrolidone maintained at 51 C. to form a solution. The solution is poured into 75 ml. cold ethanol C.) to form a suspension having -a tempera ture of about 180 C. The suspension is filtered and the collected solid washed with 6% ethanol in water at room temperature. A very fine acicular product resulted having a diameter of about 1 micron.

When subjected to a 95 C. Vacuum Stability Test, a 2.3 g. sample produced 5.58 ml. gas after 20 hours and 9.08 ml. of gas after 40 hours.

When the same quantities of untreated PETN-mannitol hexanitrate were subject to the 95 C. Vacuum Stability Test, the explosive either exploded or produced 11+ ml. of gas within a period of 30 minutes.

From the foregoing description, it is apparent that I have provided processes for obtaining heat-stabilized PETN which permits its safe use in diverse applications, both comercial and military. Further, other properties, such as detonation rate, impact sensitivity, brisance, and the like, are not deleteriously effected by my inventive processes of providing heat-stabilized PETN.

Iclaim:

1. A method for producing pentaerythritol tetranitrate heat stable at 120 C. comprising dissolving dry, heat-unstable pentaerythritol tetranitrate in N-methyl-Z-pyrrolidone maintained at elevated temperatures to form a solution,

pouring said solution into a liquid selected from the group consisting of water and alcohols to form a .suspension,

filtering said suspension to collect a solid,

washing said solid and drying said washed solid to obtaln .said heat-stable pentaerythritol tetranitrate. 2. The method of claim 1 wherein said dry, heat-unstable pentaerythritol tetranitrate is present in an amount of about grams,

said N-methyl-Z-pyrrolidone is present in an amount ranging between about 10 to 20 grams maintained at a temperature of about 40 C., and

said liquid comprises about 100 ml. of distilled water maintained at about 20 C.

3. The method of claim 1 wherein said dry, heat-unstable pentaerythritol tetranitrate is coated with about 0.2 Weight percent of polyvinyl pyrrolidone having a molecular weight of about 90,000.

4. The method of claim 1 wherein said dry, heat-unstable pentaerythritol tetranitrate is co-dissolved with about 0.8 weight percent of polyvinyl pyrrolidone in said N-methyl-Z-pyrolidone,

said polyvinyl pyrolidone having a molecular weight of about 90,000.

5. The method of claim 3 wherein said dry, heat-unstable pentae rythritol tetranitrate and said N-methyl-Z- pyrolidone are present in an amount of about 10 g. each,

said elevated temperatures range between about to C., and

said liquid comprises about 50 ml. ethanol maintained at a temperature of about 20 C.

6. The method of claim 3 wherein said coated heatunstable pentaerythritol tetranitrate is co-dissolved with about 0.6 weight percent of a stabilizer having a structure 7. A method for producing pentaerythritol tetranitratemannitol hexanitrate heat stable at C. comprising the steps of coating a mixture of heat-unstable pentaerythritol tetranitrate and mannitol hexanitrate each with polyvinyl pyrrolidone,

dissolving said coated mixture in Nmethyl-2-pyrrolidone to form a solution,

pouring said solution into a liquid selected from the group consisting of water and alcohols to form a suspension,

filtering said suspension to collect a solid,

washing said solid and drying said washed solid to obtain heat-stable pentaerythritol tetranitrate-mannitol hexanitrate.

8. The method of claim 7 further characterized by said heat-unstable PETN being present in an amount of about 8 grams,

said mannitol hexanitrate being present in an amount of about 2 grams,

said polyvinyl pyrrolidone having am olecular weight of about 90,000 and being present in an amount of about 0.2 weight percent of said heat-unstable PETN and mannitol hexanitrate, and

said N-methyl-2-pyrrolidone being present in an amount of about 15 grams.

References Cited by the Examiner UNITED STATES PATENTS 2,154,552 4/1939 Wyler 149--93 X 2,867,647 l/1959 Gow et a1. 149-93 X 3,097,122 7/1963 Cox et -al 14993 X L. DEWAYNE RUTLEDGE, Primary Examiner.

S. I. LECHERT, JR., Assistant Examiner. 

1. A METHOD FOR PRODUCING PENTAERYTHRITOL TETRANITRATE HEAT STABLE AT 120*C. COMPRISING DISSOLVING DRY, HEAT-UNSTABLE PENTAERYTHRITOL TENTRANITRATE IN N-METHYL-2-PYRROLIDONE MAINTAINED AT ELEVATED TEMPERATURES TO FRM A SOLUTION, POURING SAID SOLUTION INTO A LIQUID SELECTED FROM GROUP CONSISTING OF WATER AND ALCOHOLS TO FORM A SUSPENSION, FILTERING SAID SUSPENSION TO COLLECT A SOLID, WASHING SAID SOLID AND DRYING SAID WASHED SOLID TO OBTAIN SAID HEAT-STABLE PENTAERYTHRIOTOL TETRANITRATE.
 3. THE METHOD OF CLAIM 1 WHEREIN SAID, DRY, HEAT-UNSTABLE PENTAERYTHRITOL TETRANITRATE IS COATED WITH ABUT 0.2 WEIGHT PERCENT OF POLYVINLY PYRROLIDONE HAVING A MOLECULAR WEIGHT OF ABOUT 90,000. 